The UV and X-ray Observations of AGN Outflowsand their Influence on the Surrounding IGM

Gerard Kriss

STScI

Collaborators: J. Scott, R. Green, J. Hutchings, N. Arav, M. Brotherton, J. Gabel, J. Kaastra, M. E. Kaiser, K. Sembach, W. Zheng

Absorption-trough Frequency in Quasars

Narrow absorption troughs are more common.

Perhaps at low levels the BAL and associated absorbers are related phenomena.

Reichard et al. (2003)

The Influence of AGN Outflows

They may affect dispersal of heavy elements into the IGM and ICM. [Cavaliere et al. 2002; Adelberger et al. 2003; Granato et al. 2004; Scannapieco & Oh 2004]

They influence the ionization structure of the IGM. [Kriss et al. 1997]. They are intertwined with the evolution of the host galaxy.

[Silk & Rees 1998; Wyithe & Loeb 2003]. We still aren’t sure how the outflows are created, what structure

they have, or how much mass and energy they carry.• A key question: do the outflows escape the confines of the host galaxy?

Crucial to understanding the workings of the central engine:• Accretion process• Total energy budget

Low-redshift AGN are the nearest and brightest. We can study these at the highest angular scales and best S/N.

A Survey of Low-Redshift AGN with FUSE

104 AGN observed with FUSE (as of 11/01/02); 57 have z < 0.15. Low-luminosity AGN are bluer than high-luminosity AGN: Scott et

al. (2004). Their spectral energy distributions are broadly consistent with

accretion disk models (Shang et al. 2004). In the low-z sample (for which O VI is in the FUSE bandpass):

• 87 spectra of 57 unique AGN• 53 Type 1• 4 Type 2

Strong, broad O VI emission is visible in all Type 1 AGN Over 50% (30/53) show intrinsic O VI absorption.

• No intrinsic Lyman limits.

• No intrinsic H2 absorption. (NH2 < 1016 cm–2 in NGC 4151.)

O VI Absorption-Line Morphologies

Ly + O VI

O VILy

O VILy

Single, isolated lines. (10/30)

Multiple, blended lines. (13/30)

Broad, blended trough. (7/30)

Absorption is Common at All Luminosities

All FUSE AGN

FUSE AGN with Absorption

Outflow Velocity Increases with Luminosity

FUSE & STIS Spectra of Mrk 279

Gabel et al. (2004)

Complex, multi-component blended lines visible in the Lyman series, O VI, C IV, and N V.

The lines are saturated.

The absorbing gas only partially covers the underlying emission.

Geometry of the Absorbers in Mrk 279

The absorption only partially covers the emission.

Solve for velocity-dependent optical depths of the absorbers and the covering fractions of the emission lines and the continuum as independent variables.

The continuum is fully covered by the absorption.

The broad emission lines are only partially covered.

The absorbers are exterior to the BLR, and

They have sizes larger than the continuum emitting region.

Gabel et al. (2004)

Where is the Outflowing Gas?

Thermally driven wind from the obscuring torus (Krolik & Kriss 1995, 2001).• Gas should lie at radii of ~1 pc, depending on central luminosity.• It should be visible both in emission/reflection and in absorption.• Outflow velocities will be on the order of hundreds of km/s.

Winds from the accretion disk, either magnetically driven (Königl & Kartje 1994; Proga 2000) or radiatively driven (Murray et al. 1995; Proga 2000).• Gas should lie at distances of 1015 cm.• Terminal outflow velocities can be high, tens of km/s.

The Elvis Quasar Model (2000)

Broad OVI and Ly Absorption in NGC 4151

Molecular Gas Illuminated by UV Radiation

In AGN, X-ray absorption may be produced by a hot, tenuous background medium evaporated from the obscuring torus and driven outward as a thermal wind.

Denser clumps embedded in this medium will be cooler, with lower ionization parameter. These clumps may produce the multiple component UV absorption lines.

Thermally Driven Winds

From Krolik & Kriss (2001):

Photoionized evaporation in the presence of a copious mass source locks the ratio of ionizing intensity to gas pressure () at a critical value.

Gas at a wide range of temperatures can coexist in pressure equilibrium.

Range of marginally stable equilibria

Broad range of Ionization Parameters in NGC 3783

Netzer et al. (2003)

Several ionization stages of S and Si are all present.

The best-fitting set of models are all distributed along the vertical, marginally stable branch of the equilibrium curve, as suggested by Krolik & Kriss (2001).

Monitoring Observations are the Key

Gabel et al. (2005)

“Team NGC 3783” used Chandra, STIS, and FUSE to monitor NGC 3783 over 23 months from 2000 to 2002.

NGC 3783–UV vs. X-ray Absorption

Gabel et al. (2003)

From Gabel et al. (2003):

The UV (Ly) and X-ray (OVII) absorption have similar kinematics.

Ionization/Recombination Times Density

From Gabel et al. (2005):

Modeling the response to flux variations gives the gas density.

Gas density + photoionization models give the distance of the gas.

For Component 1 in NGC 3783, the gas lies at a radial distance of ~25 pc.

Gabel et al. (2005)

NJ=2/NJ=0 = 2.9

C III 1176—a Density Diagnostic

Gabel et al. (2005)

C III 1176—a Density Diagnostic

NJ=2/NJ=0 = 2.9

Gabel et al. (2005)

Most AGN Outflows Arise near the NLR

Two measures of density from the NGC 3783 campaign place the gas at tens of parsecs from the nucleus (Gabel et al. 2005).

Monitoring of absorption variability in NGC 4151 also suggests distances of tens of parsecs (Kriss et al. 1997; Espey et al. 1998).

Kinematics of the UV absorbers are similar to those of the NLR (Crenshaw & Kraemer 2005).

But, does the gas escape?• Velocities are high enough …• But entrainment, mass loading, and confinement can prevent it—

• The extended NLR of NGC 4151 appears to be at a standstill at 290 pc (Crenshaw et al. 2000).

Summary

Outflows are common in AGN. More than half show outflowing absorbing gas in both the UV and the X-ray.

Outflow velocities are typically hundreds to thousands of km/s.

Outflows typically show a broad range of temperatures and ionization parameters in the absorbing gas.

• Most UV absorption is due to lower ionization, lower column density gas than that causing the X-ray absorption.

UV-absorbing gas is due to higher density clumps embedded in an X-ray absorbing wind?

Possible origins for the outflowing gas range from the accretion disk to the obscuring torus.

• High-velocity, broad troughs may originate in a disk wind.• Lower velocity, associated absorbers may originate in a thermal wind from

the torus. But, the outflows may rarely escape the confines of the host galaxy …